1. Field of the Invention
The present invention relates to AC-to-DC voltage conversion circuitry, and in particular, to such conversion circuitry for use in charging a capacitance to a high voltage.
2. Related Art
With increasing use of portable electronic devices, uses of rechargeable batteries has increased as well. As portable devices become smaller, further size reductions are limited by the energy storage elements (e.g., batteries), which must be of a minimum size to provide the necessary power. Further, minimum battery sizes are further dictated by the need for such batteries to last for a minimum desired time of use. As is well known, charging and discharging of chemical-based batteries are limited by the chemistry of the batteries. In particular, charging a chemical-based battery takes a relatively long time (e.g., hours), since the charging process involves the reversal of one or more chemical processes.
However, with the development of supercapacitor technology, it is possible to use a high-voltage, high-density supercapacitor as a major energy storage element. A supercapacitor, known for its fast charging and discharging capabilities (e.g., seconds), is a physical capacitor with energy (=½CV2) stored when a DC voltage is applied. Therefore, the energy density is determined by both the capacitance (C) and the maximum voltage (V). With the energy density of supercapacitors approaching that of chemistry-based batteries, it is becoming more advantageous to develop charging solutions for them.